Under certain conditions production of new cochlear hair cells can be reactivated, after terminal mitosis, in mature damaged ears. The proposed research aims to study the neural and functional consequences of such post-mitotic production in a mature animal. The project has two overall objectives: 1) to determine whether the newly produced hair cells are innervated and 2) to determine what the functional status of the auditory system is after hair cell regeneration. Preliminary results suggest that some active process may be involved in re-innervation of newly produced hair cells such that the mature innervation ratio may be disrupted following hair cell regeneration. Histological analysis (transmission electron microscopy and immunocytochemistry) will be performed at various time intervals following either acoustic trauma or ototoxic drug administration to investigate neural synaptic activity and innervation patterns on newly produced hair cells. Finally, electrophysiological testing of auditory sensitivity (CAP absolute thresholds) selectivity (tuning curves) and linearity (input/output function) will be performed to investigate the functional significance of a newly re-populated sensory epithelium in mature birds. It is believed that these experiments will provide insight into the complex neural and functional ramifications of sensory cell regeneration in mature ears.